Equipment carrying fluid from one location to another can be susceptible to fouling by wax. A layer of wax may deposit on walls facing the space inside the equipment in which such fluid is carried. Deposition of wax can be a particular problem in the oil and gas production industry, where wax may precipitate from a fluid from a well as it is carried through a pipeline away from the well and is cooled. In a subsea location, for example, the fluid from the well may have a temperature near the well head of around 80 to 120 degrees Celsius and may cool by transfer of heat via the walls of the pipe to the surrounding seawater to a temperature close to the temperature of the seawater, as the fluid is conveyed through the pipe.
This can be a particular issue where the fluid from the well needs to be transported long distances to a downstream processing facility or where significant cooling may otherwise occur between the well head and such a facility.
Deposits of wax can cause pipeline blockage which is undesirable.
In order to avoid or reduce wax deposits on the inner surface of pipes, techniques have been developed that seek to keep the temperature of the fluid above the threshold temperature at which wax precipitates from the particular fluid concerned i.e. the “Wax Appearance Temperature” of the fluid, all the way to the processing facility. Such techniques involve applying insulation and/or electrical heating to sections of the pipeline to keep the fluid sufficiently warm. However, techniques of applying insulation and/or heating may have drawbacks in terms of logistics and/or cost particularly where a pipeline is to extend large distances.
Solutions have been proposed in which the flow of fluid from the well is conditioned near the well head by deliberately generating wax which is then released from the wall and carried in the fluid in the form of wax particles, in a so-called “cold flow”, to a downstream facility. Once the wax is produced and then released into the fluid to form the cold flow, the wax is stabilized and tends not to deposit on the walls of the pipeline.
One such cold flow technique is described in the PCT patent publication WO2009/051495. In this technique, oil from a well may be cooled to a low temperature close to the ambient sea temperature (Tlow>Tsea) in a designated conditioner section of the pipeline and wax is allowed to form on the pipeline inner wall. Once in a while, the pipeline wall may be heated by application of a pulse of heat to the wall of the pipe. The heat pulse will melt a very thin layer of the wax at the wax/wall interface. The flow of oil in the pipeline will then tear the layer of wax off the wall, releasing it in solid form into the fluid. In this way, the wax, at least to the extent it is not melted by heating the wall, is stabilized and does not turn back to its original form after release from the heated wall so that it can travel in the oil over a long distance without re-depositing.